Convergent/divergent segmented exhaust nozzle

ABSTRACT

A segmented exhaust nozzle for attenuating noise from a jet engine without adversely impacting the operability or operability limit related performance of the engine. The exhaust nozzle includes spaced apart fan nozzle inner and outer walls which form an annular exhaust gas flow path therebetween. The fan nozzle outer wall is segmented at the downstream end. The outer wall curves inwardly towards the inner wall and then turns back away from the inner wall to form an arcuate protrusion that extends into the exhaust gas flow path forming an aerodynamic throat. Through the segmented portion of the nozzle, the outer wall then continues to curve away from the inner wall before again curving back towards the inner wall at a nozzle exit station. The nozzle exit effective area is approximately equal in cross sectional area to a conventional exhaust nozzle exit area. The inwardly curving and then segmented outwardly curving portion of the exhaust nozzle forms a geometric influction that serves to reduce noise without negatively affecting engine operability or operability limit related performance.

FIELD OF THE INVENTION

This invention relates to exhaust nozzles used with turbofan engines,and more particularly to an exhaust nozzle used with a turbofan jetengine for reducing the noise of the exhaust gasses emitted from theengine without suppressing the flow of exhaust gasses through theexhaust nozzle.

BACKGROUND OF THE INVENTION

The reduction of exhaust flow jet noise from turbofan aircraft enginesis essential to meeting current and anticipated future governmentregulatory requirements for Airplane Type Certification, as well asnumerous local airport noise ordinances. There have been many attemptsto accomplish jet exhaust noise reduction through various modificationsto the exhaust nozzle of the engine. While many of these attempts haveproduced some degree of noise reduction, they have also resulted inadverse impacts on engine operability and/or engine operability limitrelated performance.

A jet noise reducing nozzle segment is typically triangular in planformand is contoured to increasingly immerse or extend into the exhaust flowwith distance along its length. Multiple segments attached to the exitof a conventional exhaust nozzle are typically used to form a jet noisereducing segmented exhaust nozzle. The effective flow area of theexhaust nozzle is reduced when nozzle segments are employed due to thepresence of portions of the nozzle segment projecting into the exhaustgas flow path. These portions, in effect, present additional blockage tothe oncoming exhaust gas flow. On a turbofan engine, the additionalblockage results in reduced fan flutter margin which can negativelyimpact fan aero-elastic structural stability. It also can causeincreased exhaust gas temperatures which can negatively impact turbinelife. Still further, it can result in reduced engine compressor stallmargin which can negatively impact engine core operation stability.Individually or together, these impacts can be of such significance thatthey prevent the implementation of the noise-reducing device on a jetengine. This impact is particularly hard felt on older jet enginedesigns that have been “thrust bumped” to near their operational limits.

With ever increasing stringency of new community noise limitations,existing aircraft types currently in service, as well as new designs forfuture aircraft, will require new jet noise control technology. Thisincreased stringency could potentially present a threat to theintroduction of future aircraft designs. Moreover, ever strictercommunity noise limitations, if not addressed by suitable noisereduction technology, could impede the introduction of derivativeaircraft platforms.

Accordingly, there exists a need to further reduce the noise produced byturbofan jet aircraft engines without imposing an unacceptable reductionin engine operability margins or operability limit related performance.

SUMMARY OF THE INVENTION

The present invention is directed to a segmented exhaust nozzle thateffectively reduces the exhaust jet noise generated by a turbofan jetaircraft engine without adversely impacting engine operability oroperability limit related performance. The exhaust nozzle is formed by afan inner wall and a fan outer wall. The inner and outer wallscooperatively form an annular exhaust gas flow path therebetween. Thewalls further define a nozzle throat area and a nozzle exit area fromwhich the exhaust gasses of a turbofan engine associated with theexhaust nozzle are emitted.

The exhaust nozzle of the present invention provides a first region inwhich one of the inner or outer walls curves gradually towards theother, thereby presenting reduced cross-sectional area to exhaust gasflow in this region forming an aerodynamic throat. A second region,through the segmented portion of the nozzle and downstream of the firstregion, is formed by the one wall curving away from the other wall toproduce a region of increased cross-sectional area to exhaust gas flow.Importantly, the second region forms an exhaust gas nozzle exit areawhich has an effective cross sectional area approximately equal to aconventional exhaust gas nozzle exit area. This is in contrast topreviously developed, segmented exhaust nozzles in which the exhaust gasnozzle exit area is smaller in cross section than a conventional exhaustnozzle exit area. This difference effectively serves to eliminate thenegative impact on engine operability and operability limit relatedperformance introduced by previous segmented exhaust nozzleconfigurations while still providing a significant reduction in enginejet noise.

The present invention thus reduces significantly the exhaust gas flowsuppression that would typically be present with previous forms ofsegmented exhaust nozzles by presenting a geometric inflection throughthe flow control region of the nozzle. The inflective profile creates aconversion-divergent, cross sectional shape to the nozzle wall. Theresult is a net zero change in exhaust flow characteristic and a netzero change in segmented nozzle noise suppression effectiveness.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limited the scopeof the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a highly simplified side view of an exhaust nozzle inaccordance with a preferred embodiment of the present invention;

FIG. 2 is a highly simplified cross sectional view of a portion of anexhaust nozzle in accordance with section line 2—2 in FIG. 1illustrating the curvature of the convergent/divergent segmented exhaustnozzle of the present invention;

FIG. 3 is a bar graph illustrating test results for noise reductionunder various operating conditions;

FIG. 4 is a graph illustrating the overall sound pressure level relativeto a body station of an aircraft; and

FIG. 5 is a graph illustrating the nozzle discharge characteristic ofthe segmented exhaust nozzle of the present invention as compared tothat of a conventional exhaust nozzle flow characteristic and the flowcharacteristic of previous designed segmented nozzles.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiment(s) is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses.

Referring to FIG. 1, there is shown a segmented exhaust nozzle 10 inaccordance with a preferred embodiment of the present invention. Theexhaust nozzle 10 is particularly adapted for use with high bypass ratioturbofan jet engines. In this example, an external plug 11 is disposedwithin a housing structure forming a nacelle 18 along an imaginary axialcenter line “C_(L)” of the nacelle.

Referring to FIG. 2, there is shown a portion of the segmented exhaustnozzle 10. The segmented exhaust nozzle 10 includes a fan nozzle innerwall 12 and a fan nozzle outer wall 14 spaced apart from the inner wall12. Cooperatively, the walls 12 and 14 form an annular exhaust gas flowpath 16. The exhaust nozzle 10 is further typically contained within thenacelle 18, which also houses the turbofan jet engine (not shown).

The outer wall 14 of the segmented exhaust nozzle 10 comprises a uniquecontour which effectively serves to reduce the exhaust jet noisegenerated by the turbofan jet engine without negatively impacting theoperability or operability limit related performance of the engine. Theouter wall 14 includes a portion curving gradually inwardly toward theinner wall 12 from a first point 20 to a second point 22 forming anaerodynamic choke point, or choke flow control region. From point 22,the outer wall 14 changes direction and curves gradually away from theinner wall 12 to a third point 24. Thereafter, the outer wall 14 againbegins to curve towards the inner wall 12 to a fourth point 26. This isthe segmented region of the nozzle. Point 22 also defines the locationof the exhaust nozzle throat area (“A_(throat)”) while an integration ofpoints 24 through 26 comprises the segmented exhaust nozzle exit area(“A_(exit)”). For comparison purposes, “A_(E1)” defines a point at whicha conventional exhaust nozzle exit area would be located. Also, “A_(E1)through A_(E2)” defines an exhaust nozzle exit area for a previouslydeveloped, typical segmented exhaust nozzle.

From FIG. 2 it can be seen that points 20-24 define a first region inwhich the outer wall 14 forms an arcuate protrusion which projects intothe exhaust gas flow path 16. The axial distance between points 24 and26 defines a region of increased cross-sectional area to the exhaust gasflow. It will also be appreciated that the edge of region two, points 24through 26, provides an effective cross sectional area, represented bythe imaginary line 26, which is approximately equal to A_(E1), but stilllarger than A_(E2). The entire wall structure between points 20 and 26can be viewed as forming a geometric inflection in the exhaust gas flowpath 16. The area between points 22 and 24 presents an increasedcross-sectional area to the exhaust gas flow, thereby reducing blockage.The subsequent curvature back towards the inner wall 12 serves torealign the flow of exhaust gasses to maximize the nozzle noisereduction efficiency. The result is a segmented nozzle with distinctsonic and subsonic flow control regions yielding a net zero change inflow characteristic and a net zero change in segment noise suppressioneffectiveness of the segmented exhaust nozzle 10.

While it will be appreciated that the outer wall 14 of the exhaustnozzle 10 has been illustrated as including the geometric influctionsurface, it will be appreciated that this surface could also be providedon the inner wall 12 of the exhaust nozzle 10.

Referring to FIG. 3, a graph 30 illustrates the reduction in exhaust gasflow noise with the segmented exhaust nozzle 10 of the present inventionduring a flight test.

FIG. 4 is a graph 32 illustrating the reduction in interior noise of anaircraft incorporating the segmented exhaust nozzle 10 of the presentinvention.

FIG. 5 illustrates a graph 32 of the flow characteristic of thesegmented exhaust nozzle 10 of the present invention as compared to aconventional exhaust nozzle flow 34 and a flow characteristic of apreviously developed, segmented nozzle design 36. From FIG. 5 it will beappreciated that the flow characteristics of the exhaust nozzle 10closely match those of a conventional exhaust nozzle.

It will be appreciated then that the segmented exhaust nozzle 10 of thepresent invention provides a means to significantly attenuate theexhaust jet noise produced by turbofan engines, and thus help to meetincreasingly stringent community noise requirements. Importantly, theexhaust nozzle 10 does not adversely impact the operation or operabilitylimit related performance of existing large turbofan jet engines.

The segmented exhaust nozzle 10 is further capable of being used as asegmented nozzle in exhaust nozzles having an internal primary plug,such that no inner wall is present. In such an exhaust nozzle, the outerwall 14 would curve with reference to the imaginary center line C_(L),since no inner wall would be present.

Those skilled in the art can now appreciate from the foregoingdescription that the broad teachings of the present invention can beimplemented in a variety of forms. Therefore, while this invention hasbeen described in connection with particular examples thereof, the truescope of the invention should not be so limited since othermodifications will become apparent to the skilled practitioner upon astudy of the drawings, specification and following claims.

What is claimed is:
 1. A segmented flow nozzle for use with a jet engine to inhibit jet noise emitted from the jet engine, said flow nozzle comprising: a circumferential nozzle inner wall; a circumferential nozzle outer wall spaced apart from said inner wall to define an annular flow path therebetween; one of said inner and outer walls curving toward the other to define a protrusion, at a first region of said exhaust gas flow path, which that extends into said flow path to reduce a cross sectional area of said flow path, thereby forming a choke flow control region; said flow nozzle including a segmented region downstream of said choke flow control region; through the segmented region of the nozzle, said one wall gradually curving away from the other, and then back toward the other, to provide an increased cross-sectional area for un-choked flow control; and a downstream edge of said segmented region defining a nozzle exit area having an effective cross sectional area approximately equal to a non-segmented nozzle exit area.
 2. The nozzle of claim 1, wherein a midpoint of said segmented region defines a cross sectional area which is larger than said non-segmented nozzle exit area.
 3. The nozzle of claim 1, wherein said nozzle forms an extension of an existing nozzle structure.
 4. A segmented exhaust nozzle for use with a jet engine to inhibit exhaust jet noise emitted from the jet engine, said exhaust nozzle comprising: a circumferential nozzle inner wall; a circumferential nozzle outer wall spaced apart from said inner wall to define an annular exhaust gas flow path therebetween said circumferential nozzle outer wall, in cooperation with said circumferential nozzle inner wall, forming a plurality of spaced apart segmented regions of the exhaust nozzle; said outer wall curving toward the inner wall, to define a arcuate protrusion that extends into said exhaust gas flow path to reduce a cross-sectional area of said annular exhaust gas flow path and thereby provide a choke flow control region along the annular exhaust gas flow path; said segmented regions being disposed downstream of said choke flow control region; said outer wall gradually curving away from the inner wall, and then back toward the inner wall, to define regions downstream of said arcuate protrusion for providing increased cross-sectional area for un-choked flow control to said exhaust gas flowing through said annular exhaust gas flow path; and wherein an edge of said downstream region defines a nozzle exit having an effective cross sectional area approximately equal to a non-segmented exhaust nozzle exit area.
 5. The exhaust nozzle of claim 4, wherein a midpoint of said region defines a larger cross sectional area than said edge of each said region.
 6. The exhaust nozzle of claim 5, wherein said midpoint defines a larger cross sectional area than said conventional exhaust nozzle exit area.
 7. A segmented exhaust nozzle for use with a jet engine exhaust nozzle structure, said exhaust nozzle comprising: a nozzle inner wall; a nozzle outer wall spaced apart from said nozzle inner wall; said nozzle inner and outer walls forming said exhaust nozzle and having a nozzle throat area and a nozzle exit area downstream from said nozzle throat area; at least one of said nozzle inner and outer walls curving gradually toward the other from a first point to a second point positioned downstream of said first point, relative to flow through said jet engine, to thereby reduce a cross sectional area between said nozzle walls to form an aerodynamic throat area of said segmented exhaust nozzle; said exhaust nozzle including a plurality of segmented regions downstream of said throat area; through each said segmented region of the exhaust nozzle, said at least one of said walls then curving gradually away from the other from said second point to a third point downstream of said second point, relative to said flow through said jet engine, to thereby effectively increase the cross sectional area presented to the flow within said segmented exhaust nozzle, and wherein an intermediate point between said second and third points defines where a conventional nozzle exit point is located on a non-segmented exhaust nozzle; further through the segmented region of the nozzle downstream of said third point, said at least one of said walls then curving gradually toward the other from said third point to a fourth point downstream of said third point, relative to said flow, to thereby reduce a cross sectional distance between the walls within said segmented exhaust nozzle at said fourth point; and wherein said cross sectional area integrated between said third point and said fourth point is effectively equal to a cross section area at said intermediate point.
 8. The exhaust nozzle of claim 7, wherein a region between said first and second points represents an arcuate protrusion to accelerate said flow.
 9. The exhaust nozzle of claim 7, wherein a region between said second and fourth points presents increased cross sectional area for subsonic flow control.
 10. A segmented exhaust nozzle for use with a jet engine fan exhaust nozzle structure, said exhaust nozzle comprising: a fan nozzle inner wall; a fan nozzle outer wall spaced apart from said fan nozzle inner wall to form an annular exhaust gas flow path; said exhaust nozzle having a nozzle throat area and a nozzle exit area downstream from said nozzle throat area; said outer wall curving gradually toward the inner wall from a first point to a second point positioned downstream of said first point, relative to exhaust gas flow through said nozzle, to thereby reduce a nozzle throat cross sectional area of said exhaust nozzle and accelerate said exhaust gas flow therethrough; said exhaust nozzle including a segmented region downstream of said second point; through said segmented region of the nozzle, said outer wall then curving gradually away from the inner wall from said second point to a third point downstream of said second point, relative to said exhaust gas flow, to thereby effectively increase the cross sectional area presented to said exhaust gas flow within said exhaust nozzle; wherein an intermediate point between said second and third points defines where a conventional nozzle exit point is located on a non-segmented exhaust nozzle; and said outer wall then curving gradually toward the inner wall from said third point to a fourth point downstream of said third point, relative to said exhaust gas flow; and wherein said cross sectional area integrated through said third point and said fourth point is effectively equal to a cross section area at said intermediate point.
 11. The exhaust nozzle of claim 10, wherein a region between said first and third points defines an arcuate protrusion.
 12. A segmented nozzle for use with a jet engine to inhibit jet exhaust noise emitted from the jet engine, said exhaust nozzle comprising: a nozzle outer wall spaced apart from an imaginary axial center line of said nozzle; said outer wall curving toward said imaginary axial center line to define a protrusion that extends into said exhaust gas flow path to reduce a cross sectional area of said exhaust gas flow path, thereby forming a choke flow control region; said nozzle including a segmented region downstream of said choke flow control region; through the segmented region of the nozzle, said outer wall gradually curving away from said imaginary axial center line, and then back toward said center line, to define said segmented region, which provides an increased cross-sectional area for un-choked flow control; and a downstream edge of said second region defining a nozzle exit area having an effective cross sectional area approximately equal to a non-segmented exhaust nozzle exit area.
 13. A segmented flow nozzle for use with a jet engine to inhibit engine noise emitted from the engine, said flow nozzle comprising: a nozzle inner wall; a nozzle outer wall spaced apart from said inner wall to define a flow path therebetween; one of inner and outer walls curving toward the other at a first region of said flow path to reduce a cross sectional area of said flow path; and form a choke flow control region; the segmented region being downstream of said choke flow control region; through the segmented region of the nozzle, one of said inner and outer walls curving away from the other, and then back toward the other, to define said segmented region such that said segmented region has said walls diverging from one another and then converging toward one another in a direction of said flow through said jet engine; and a downstream edge of said segmented region defining a nozzle exit area having a cross sectional area approximately equal to a non-segmented jet engine nozzle exit area.
 14. A method for inhibiting noise emitted from a jet engine, comprising: using a nozzle inner wall and a nozzle outer wall to form a segmented flow nozzle that provides a flow path therebetween for an exhaust flow through said jet engine; defining a first flow region within said flow nozzle having a first cross sectional area that acts as a constriction in said flow path; and thereby forms a choke flow control region; defining a segmented nozzle region downstream of said choke flow control region, relative to a direction of airflow through said flow path, which has a second cross sectional area and a third cross sectional area, wherein said second cross sectional area is larger than said first cross sectional area; and forming a downstream edge of said segmented nozzle region such that a nozzle exit area thereof has an effective cross sectional area approximately equal to that of a non-segmented nozzle exit area. 